In steam generating systems, a condenser is used downstream of a steam turbine to convert steam, after it has passed through the steam turbine, from its gaseous state to its liquid state. The condenser may be air-cooled and comprises a steam inlet duct, a plurality of condenser tubes, and a condensate outlet duct. Steam passes into the condenser through the steam inlet duct and flows through the condenser tubes. Air is forced over outer surfaces of the tubes so as to cool the tubes and, hence, the steam flowing through the tubes, thus causing the steam to be converted into a liquid condensate. The condensate is reused in generating steam for the steam turbine such that at least a portion of it later returns to the condenser where it is once again converted to its liquid state in the condenser.
It is desirable to prevent contaminants, such as oxygen and carbon dioxide, from entering the condenser. When the concentrations of oxygen and carbon dioxide are high enough, they become corrodents to iron and steel used in the condenser and other components of the steam generating system, including piping and a steam generator. The corrosion product is iron oxide which tends to deposit on the steam generator surfaces and reduce heat transfer. Corrosion also causes wall thinning of the condenser tubes and other steel structures, and can result in leaks and failures. In addition to being a corrodent, carbon dioxide interferes with monitoring of the steam generating system for more corrosive species, such as chloride. Hence, carbon dioxide is a nuisance that may require the steam generating system to use more sophisticated monitoring equipment at significantly greater expense.
Despite attempts to prevent the leakage of contaminants into steam generating systems, during certain operating conditions of the steam generating systems, some leakage may occur. For example, the normal operating pressure in a typical condenser may be a few inches of mercury (absolute pressure) and, hence, the normal operating pressure is at a vacuum, i.e., less than 1 atmosphere absolute pressure, in which case contaminants may leak into the condenser. Further, contaminants may leak into the condenser of a steam generating system when the system is stopped or slowed, such as during shut-down phase of the system. Additionally, various maintenance procedures that may be performed during the system shut-down phase require that one or more of the components of the steam generating system be filled with air, i.e., so that a human may enter into the component to perform maintenance thereto.
Condensate polishers and/or deaerators are known to remove contaminants from the condensate. However, as noted above, the normal operating pressure within a typical condenser in a power generating system is below one atmosphere, and thus, contaminants are susceptible to leak into the condenser. Thus, the condensate polishers/deaerators used to remove contaminants from the condensate may be continually run during operation of the power generating system, thus increasing a cost and/or decreasing an efficiency of the power generating system.